Controls in some form or another are included in nearly every vehicle to allow a user or vehicle operator to direct operation of the vehicle. Common to most vehicles are several controls: steering control, drive control, and braking control. Using these individual controls, a vehicle operator may steer the vehicle in a desired direction, control forward or reverse movement, accelerate or decelerate the vehicle, and stop the vehicle. Additional, separate controls in one form or another have also been incorporated into vehicles. Examples of such controls include emergency braking, lighting, and transmission gear selection.
One type of vehicle that has become prevalent for its enhanced reliability and increased power is a hydrostatically powered vehicle. This vehicle type includes a hydrostatic transmission or hydraulic drive system to provide forward and reverse motion. Conventional hydraulic drive systems use pressurized hydraulic fluid to drive a hydraulic motor, which converts the hydraulic pressure and flow into torque and angular displacement. In many cases, unlike the combination of an internal combustion engine and a geared transmission often times used in passenger vehicles, conventional hydrostatic transmissions do not utilize a gearbox. To the vehicle operator, this may mean there is no need to select gears or operate a clutch, thereby simplifying operation of the vehicle.
Steering and speed control in conventional hydrostatically powered vehicles are accomplished by independently powered drive wheels on each side of the vehicle. One drive wheel may be operated in one direction at one speed while the other wheel is operated differently, such as at a different speed or a different direction, or both. This may cause the vehicle to turn in a desired direction. To control the independent operation of the drive wheels, the vehicle is often times fitted with one or more control levers that the vehicle operator can move independently to control the speed and direction of each wheel.
Dual control levers or twin stick controls may be provided in proximity to each other, with each lever or stick controlling one of the drive wheels. Advancing both levers together in a forward direction from a neutral position may result in both drive wheels rotating to provide forward motion. Further advancing each lever forward increases the drive speed of the respective wheel. Conversely, moving each lever back toward the neutral position from the forward position decreases the drive speed of the respective wheel. Advancing both levers together in a reverse direction from the neutral position (or toward the vehicle operator) may result in both drive wheels rotating to provide reverse motion. Similar to moving the levers forward, the amount of displacement of each lever from the neutral position may correspond to the speed of the respective wheel.
Although a hydrostatic vehicle with dual control levers is typically configured to remain motionless while both control levers are in the neutral position, unwanted motion may occur due to inadvertent movement of the levers, or due to improper calibration of the hydrostatic transmission. As an added precaution against unwanted motion, conventional hydrostatically powered vehicles include a separate manual brake that, when set, actively prevents motion of the vehicle. To set the separate manual brake in a conventional hydrostatically powered vehicle, the vehicle operator first releases one or both of the control levers, and then actuates the manual brake to prevent motion of the vehicle. During this time, one or both of the control levers are out of the vehicle operator's control, thereby creating a circumstance in which unwanted motion could occur. Additionally, unwanted motion could also occur if the vehicle operator forgets to set the manual brake.
Another feature that has been introduced to conventional hydrostatic vehicles to enhance safety is a separate neutral lockout. The neutral lockout prevents starting of the vehicle if the controls are not in the neutral position. In this way, the vehicle can be prevented from moving in response to starting when the control levers are likely not under control by the vehicle operator.
Yet another feature common to many hydrostatic vehicles is operator presence detection. Conventionally, operator presence detection is achieved by using a sensor or switch sensitive to weight or force applied to the operator's seat or pedestal. Presence or absence of the operator can be determined based on whether the operator's weight is detected on the seat or pedestal. For example, if the operator's weight is detected on the seat or pedestal, the vehicle may allow starting, and continue running. Once the operator's weight is no longer detected, the vehicle may disable operation. As can be seen, this functionality is dependent on weight of the operator, and use of additional sensors or switches separate from the vehicle controls.